Family: Rhabdoviridae

Genus: Gammaplatrhavirus

Distinguishing features

Viruses assigned to the genus Gammaplatrhavirus form a distinct monophyletic group based on well-supported Maximum Likelihood or Maximum Clade Credibility trees inferred from complete L sequences. Members of the genus have been detected in trematode flatworms (phylum Platyhelminthes), barnacles or bat tissue samples. They are distinct phylogenetically from rhabdoviruses assigned to the genera Alphaplatrhavirus and Betaplatrhavirus.

Morphology

Viruses assigned to the genus have not yet been isolated or visualized by electron microscopy.

Nucleic acid

Gammaplatrhavirus genomes consist of a single molecule of negative-sense, single-stranded RNA of 10.8–11.8 kb (Shi et al., 2018, Dheilly et al., 2022, Chen et al., 2023).

Proteins

Gammaplatrhavirus N, P, M, G and L proteins appear to be homologous with corresponding proteins of other rhabdoviruses. Gammaplatrhavirus G proteins are class I transmembrane glycoproteins. Alignment of gammaplatrhavirus G proteins with that of vesicular stomatitis Indiana virus (species Vesiculovirus indiana) indicates likely conservation of 8 of the 12 conserved cysteine residues that are typical of animal rhabdovirus G proteins  (Walker and Kongsuwan 1999, Roche et al., 2006), and two additional conserved cysteine residues that are likely to form another disulphide bridge in the folded protein. Gammaplatrhaviruses usually encode one additional protein which has the structural characteristiucs of a class I viroporin.

Genome organisation and replication

Gammaplatrhavirus genomes include the five genes (N, P, M, G and L) encoding the structural proteins and one additional gene between the G and L genes  encoding a class 1 viroporin (Figure 1 Gammaplatrhavirus).

Figure 1 Gammaplatrhavirus. Schematic representation of gammaplatrhavirus genomes in reverse (positive-sense) polarity. The five long open reading frames (ORFs) in the N, P, M, G and L genes are shown (open arrows). Additional ORFs encoding predicted class I viroporins shown in yellow.

Biology

Gammaplatrhaviruses have been detected by metagenomic sequencing of platyhelminths that parasitise invertebrate and vertebrate hosts (Dheilly et al., 2022). These include the trematode worms (Clonorchis sinensis, Metorchis orientalis and Dicrocoelium dendriticum). Other gammaplatrhaviruses have been detected by metatranscriptomic sequencing of barnacles or bats (Shi et al., 2018, Chen et al., 2023). No isolates are currently available for any of these viruses. Available evidence suggests that those gammaplatrhaviruses detected in invertebrates or vertebrates are likely due to platyhelminth infestation.

Species demarcation criteria

Viruses assigned to different species within the genus have several of the following characteristics: A) minimum amino acid sequence divergence of 10% in N proteins; B) minimum amino acid sequence divergence of 10% in the L proteins; C) minimum amino acid sequence divergence of 15% in G proteins; D) significant differences in genome organisation as evidenced by numbers and locations of ORFs; E) can be distinguished in virus neutralisation tests; and F) occupy different ecological niches as evidenced by differences in arthropod and/ or vertebrate hosts.